Wave-propagation in rocks saturated by two immiscible fluids

Abstract

Accurate modelling of the dependence of seismic wave speed from frequency and fluid content is crucial to the quantitative interpretation of seismic data. Dispersive effects such as squirt flow become important at a critical frequency that is proportional to fluid mobility. When a porous medium is partially saturated it is not clear how the respective fluid mobilities are to be averaged. Building on previous work, we use a nonzero, static capillary pressure parameter and a relative permeability model to simulate the effects of squirt flow in a realistic sand saturated by water and CO2 where the CO2 can be in either the liquid or supercritical phase. We show that the effective fluid follows a mixing law similar to Brie's empirical model and the effective frequency depends both on the relative permeability model and the capillary pressure parameter which can potentially lead to a dispersive effect in the seismic band.